Understanding Uncertainty in Cyber-Physical Systems: A Conceptual Model
Uncertainty is intrinsic in most technical systems, including Cyber-Physical Systems (CPS). Therefore, handling uncertainty in a graceful manner during the real operation of CPS is critical. Since designing, developing, and testing modern and highly sophi
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Simula Research Laboratory, Oslo, Norway {manzhang,bselic,shaukat,tao}@simula.no 2 University of Oslo, Oslo, Norway 3 ULMA Handling Systems, Oñati, Spain [email protected] 4 Future Position X, Gävle, Sweden [email protected]
Abstract. Uncertainty is intrinsic in most technical systems, including Cyber-Physical Systems (CPS). Therefore, handling uncertainty in a graceful manner during the real operation of CPS is critical. Since designing, developing, and testing modern and highly sophisticated CPS is an expanding field, a step towards dealing with uncertainty is to identify, define, and classify uncertainties at various levels of CPS. This will help develop a systematic and comprehensive understanding of uncertainty. To that end, we propose a conceptual model for uncertainty specifically designed for CPS. Since the study of uncertainty in CPS development and testing is still irrelatively unexplored, this conceptual model was derived in a large part by reviewing existing work on uncertainty in other fields, including philosophy, physics, statistics, and healthcare. The conceptual model is mapped to the three logical levels of CPS: Application, Infrastructure, and Integration. It is captured using UML class diagrams, including relevant OCL constraints. To validate the conceptual model, we identified, classified, and specified uncertainties in two distinct industrial case studies. Keywords: Uncertainty
Cyber-Physical systems Conceptual model
1 Introduction Cyber-Physical Systems (CPS) are present in a variety of safety/mission critical domains [2–4]. Given the pervasiveness of CPS and their criticality to the daily functioning of society, it is vital for such systems to operate in a reliable manner. However, since they generally function in an inherently complex and unpredictable physical environment, a major difficulty with these systems is that they must be designed and operated in the presence of uncertainty. By uncertainty we mean here the
This work is funded by the U-Test H2020 Project (www.u-test.eu). © Springer International Publishing Switzerland 2016 A. Wąsowski and H. Lönn (Eds.): ECMFA 2016, LNCS 9764, pp. 247–264, 2016. DOI: 10.1007/978-3-319-42061-5_16
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lack of certainty (i.e., knowledge) about the timing and nature of inputs, the state of a system, a future outcome, as well as other relevant factors. As a first crucial step in such an investigation, we feel that it is necessary to understand the phenomenon of uncertainty and all its relevant manifestations. This means to systematically identify, classify and specify uncertainties that might arise at any of the three levels of CPS: Application, Infrastructure, and Integration. Based on studying and analyzing existing uncertainty models developed in other fields, including philosophy, physics, statistics and healthcare [5–8], we have defined an uncertainty conceptual model for CPS (U-Model) with the following objectives: (1) provide a unified and comprehensive description of uncertainties to both researchers and practitione
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